1. Field of the Invention
This invention relates to a polymer supported chromium catalyst composition used for olefin polymerization, novel methods of producing such catalysts and methods of polymerizing and copolymerizing alpha-olefins to produce high density polyethylene polymers with high melt indices and superior morphology. This invention relates to the preparation of new catalyst formulation comprising of a chromium compound, a magnesium containing compound or an aluminum compound a metal alkoxy compound and a polymeric material support, mainly chloromethylated cross linked styrene-DVB copolymer or polyvinylchloride.
2. Description of the Related Art
The basic chromium oxide catalyst was discovered by J. P. Hogan and R. L. Banks at Phillips Petroleum. The catalyst, along with associated solution and slurry processes, was licensed worldwide and this catalyst composition still accounts for a large fraction of the high density polyethylene produced today. Phillips has continued to be active in research to improve through out the years and modified their basic catalyst, as described in U.S. Pat. Nos. 3,445,367, 3,622,521, 3,879,362, 3,950,316, 3,985,676, 3,974,101, and 4,049,896.
Many of the Phillips licensees have also followed the same pattern, and that can be seen from the volume of their patents, pursued active programs in this area. The catalyst has been further studied in a number of academic laboratories with the objective of understanding the chemistry of the active site and of the polymerization.
These catalysts consisted of a chromium (VI) oxide supported on a high surface refractory oxide support. Generally the support is amorphous microspheroidal silica. The catalyst is prepared by activating the chromium containing support at temperatures of 500° C. to 1000° C. in a dry, oxygen containing atmosphere. Modifying materials such as titanium and fluoride are generally added prior to the activation.
A large number of chromium compounds can be used in the preparation of these catalyst, all are presumably converted to Cr(VI) oxide under these activation conditions. Chromium (VI) oxide (CrO3) is itself unstable at temperatures above 350° C. and decomposes to chromium (III) oxide (Cr2O3) and oxygen. This leads to the conclusion that Cr (VI) species in the catalyst after activation is not a simple Cr2O3, but the product of an interaction of the chromium (III) oxide with the support surface. One such proposed product is a surface chromate ester.
Also, despite the extensive use of the described supports for olefin polymerization catalysts, the support materials themselves have several deficiencies. For example, in the case of chromate silica high calcinations temperatures in the range 500° C. to 1000° C. are required for the following: (1) oxidizing all Cr species present to Cr (VI) species, (2) removals of all organic & volatile materials, (3) removals of most chemically bound water from the silica surface, (4) completing ionic association of chromium and modifiers with silica.
This represents a significant portion of the preparation time of the catalyst. Further, silica supported this way is typically done by contacting silica with chromium compound prior to the deposition of the titanium component.
This procedure is usually troublesome. Also, the use of silica as a support results in the support remaining largely in the product, which can affect the product properties, such as optical properties, or processing.